Image sensing apparatuses, e.g., conventional digital cameras or the like, which sense, record and reproduce an image, often employ a data compression technique complying with the JPEG baseline scheme.
However, the conventional JPEG baseline scheme utilizes one quantization table for the entire image on a screen. Therefore, it is impossible to record a particular region of an image in higher quality than other regions of the image. If a user desires higher image quality for a particular region of the image, other regions must also be compressed as a high-quality image. As a result, the size of the compressed image file becomes large, and this causes problems of time-consuming data transfer or printing operation.
Furthermore, when recording time is limited, e.g., at a time of image data transfer or during a continuous photographing operation, it is preferable to keep the size of an image file small, but this raises a problem of deteriorated image quality.
Currently, so-called JPEG 2000 is under review as the next-generation compression scheme. Although detailed description will not be provided herein, the JPEG 2000 is characterized by the function of designating a region of interest (hereinafter referred to as an ROI) in an image and coding the image of the designated ROI with a different compression coefficient (compression rate) from that of other regions. This ROI function can be one of the solutions to the aforementioned problems. More specifically, in order to reproduce an image of the ROI with higher precision than other regions, a lower compression coefficient than that of other regions may be set.
However, in the case of applying the ROI function to, e.g., a digital camera or the like, designation of an ROI becomes problematic. For instance, it is extremely complicated for a user to designate the ROI each time a photograph is taken.